Aspiration pneumonitis is a disease occurring due to bacteria or the like which adhere to food, saliva, or the like when the food, the saliva, or the like enters the inside of a lung through the trachea. In addition, recently, it has become known that aspiration pneumonitis occurs similarly when foreign bodies such as gastric juice which have flowed backward from the stomach to the esophagus enter the inside of the lung through the trachea during sleep. Foreign bodies such as food are likely to enter the inside of a lung of aged people or the like due to a deteriorated swallowing function, and resisting power for discharging (expectorating) the foreign bodies which have entered the inside of the lung is weak. Therefore, in accordance with aging of the population, the number of patients suffering from pathogenesis of aspiration pneumonitis tends to increase year after year.
For example, Japanese Patent Application Nos. JP-A-2007-267999, JP-T-2009-520559, and/or JP-T-2004-538060 disclose methods in which a medical instrument such as an implantable device and a valve for inhibiting gastric juice or the like from flowing backward from the stomach to the esophagus indwells in the esophagus, the stomach, or the like, to prevent pathogenesis of reflux esophagitis caused by gastroesophageal reflux disease occurring when the gastric juice flows backward into the esophagus.